What would be a single word or phrase to describe someone who disregards society and its unwritten rules?

Rebel - noun - A person who resists or defies authority or convention.

Rebel - noun - A person who does not like rules or authority, and shows this by behaving differently from most people in society.

Rebel - noun - Someone who may behave differently from other people and has rejected the values of society or of their parents.

One classic example is the film James Dean - Rebel Without A Cause. This film is a coming of age story about a young man who rebuffs societal norms and the expectations of his parents on his path to maturity.

The word rebel has become the optimum word choice for North American English speakers who are trying to characterize a person who disregards society norms.

A recusant TFD

2. A dissenter; a nonconformist.

How about "anti-authority"? Someone who is anti-authority has a disregard for rules. You could also say "He is a law unto himself". [https://dictionary.cambridge.org/dictionary/english/be-a-law-unto-yourself][1]

to behave in a way that is independent and does not follow the usual rules for a situation: Charlie, of course, never fills in the record forms but then he's a law unto himself.

Non-conformist would be my choice as it does not have as strong connotation to proactive resistance to norms, just someone who pays them no heed. I would say a rebel would wear the opposing team's uniform to a football game whereas a nonconformist wouldn't wear any team's uniform and might be reading a book during the game.

Indocile

unwilling to accept control or instruction; unsubmissive

free spirit would be my guess at what you are looking for. Not necessarily "pleasure seeking" and not quite "wandering misdirectedly" or a pejorative.. more someone who just makes their own goals with lesss concern of normal practicalities and expectations than most

free spirit from Oxford Online dictionaries

An independent or uninhibited person.

‘they raised their children to be free spirits’

More example sentences

‘It is something of a risk because we poets are free spirits and we distrust the establishment.’

‘‘She was a free spirit who returned to community living and open spaces whenever she could,’ the congregation was told.’

‘Independent and a true free spirit, it was clearly her transient, urban upbringing that gave her this hunger for success.’

‘She's very involved in her children's upbringing and she encourages them to be free spirits.’

‘They never seemed to notice that the nomads gave every appearance of being happy, free spirits.’ ‘The character I play is a free spirit, who believes in freedom.’ ‘For the most part they're the seekers, slackers, and free spirits who tend to avoid the straight life, such as it is, for as long as they can.’ ‘They are free spirits and the show is never the same two days running.’ ‘It is not a choice of free spirits vs. control freaks.’